Extremely irrelevant is the review of a rented machine on a page selling new ones.
Just as a rented car, which has done hundreds of thousands of kilometers by all kinds of people, has nothing to do with a new one that you will get with a factory warranty, so the concentrator that has done hundreds of thousands of hours by all kinds of people - most of whom mistreat it because they do not bother to learn about its proper use - has nothing to do with a new one that you will get with a factory warranty.
Of course the rented ones make noise. They are machines that work nonstop, under adverse conditions and very often by bad users.
Also, very often they are poorly maintained by the companies to save costs. If you add to that the fact that most renters are insured by EOPYY, who instead of rent pay with prescriptions and then the companies are paid literally CRUMBS by EOPYY, so they are not enough to properly maintain the machines, you understand what is happening with the rented ones...
So is it the same? Apples - oranges.